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caeies op enamel. 81

Superficial, Spreading op Caries in Proximal Surfaces
op Bicuspids and Molars.
illustrations: figures 86-95.
We pass now to the superficial conditions as seen in the
proximal surfaces of the bicuspids and molars. If we examine
the whitened outlines seen upon the surfaces of the teeth before
any enamel rods have fallen away, we will find these decays
taking certain definite forms by reason of spreading, and often
starting at several points instead of at one central nidus. A
knowledge of these forms and the reasons for them, is of great
importance in the treatment of caries.
The group of illustrations, Figures 86-89, inclusive, shows
the principal varieties of form produced by the spreading bucco-
lingually of beginning decays in the proximal surfaces of tha
bucuspids as seen in whole teeth. This tendency is practically
the same in the molars, as seen in Figure 91. These may be
confined to a round spot, as is often the case in the incisors, as
shown in Figure 78, but the more general tendency is to spread
buccally and lingually from the beginning point. This is shown
progressively in the different pictures of this group and illus-
trates the common tendency of caries of the enamel to spread
in these particular directions. Occasionally the tendency to
spread gingivally is seen, as is illustrated in Figure 90. The
cause of this will be more explicitly discussed later. It should
be noticed particularly here that the tendency is to spread bucco-
lingually rather than gingivally, though, as will be shown
later, wide spreading gingivally occurs under certain conditions.
Spreading occlusally does not ordinarily occur, because that
part of the surface from the contact occlusally is cleaned by
mastication. As we shall see later, decays that begin much to
the gingival of the contact point may spread occlusally. These
beginning decays are characteristic of the surface areas of
beginning decays in the proximal surfaces in the bicuspids and
molars. It will be readily seen that if the cut is made horizon-
tally instead of lengthwise of the tooth, as in split teeth herein
before shown, the area of decay presented would be very dif-
ferent.
In the group of illustrations, Figures 92-95, inclusive, cross
sections are shown illustrating the conditions from that view.
Here, instead of the narrow area of decay seen in the whole
teeth, as in the group 86-91, the teeth are cut crosswise through
similar areas of decay. These have the additional value of show-